The M roadster has a fairly impressive stock exhaust–quad polished tips exit from dual mufflers and emit a mellow note. However, like anything in life, even something good can be improved. Supersprint has made aftermarket exhaust systems for BMWs for years, has been making high-quality exhaust systems since 1955, and is highly regarded. In fact, the quality of the exhaust meets TUV standards for construction and is treated as if it were an OEM exhaust in Germany, which typically is very picky about aftermarket modifications to cars.

Supersprint is based in Italy, and their official U.S. Importer is BMP Design, based in Texas. BMP carries the full Supersprint line, including the 100% stainless steel dual M roadster exhaust with quad DTM tips. The exhausts arrived in perfect condition (a feat in itself given that the shipment consisted of two 6-foot-long boxes that had to travel from Italy to BMP in Texas, and then from there to the reviewer). The packaging is first-rate, with the exhausts themselves being sealed in plastic, with special packing around the tips to preserve them, and with plenty of paper padding protecting the exhausts inside the boxes.

The pictures above exhibit the external differences between the Supersprint exhaust (left) and the stock exhaust (right). The tips are larger and upturned, the muffler itself is smaller, and the whole system is bead-polished to a high shine. As the arrow shows, the Supersprint exhaust also features straighter pipe between the fitting (which will be attached just behind the catalytic converter) and the muffler.

A side note: When arranging for a place to install the Supersprint exhaust, it may be best to also arrange for a friend with either a sports utility vehicle or a pickup truck to be available to help you transport the new exhaust to the installation location, and to help you transport the old exhaust home.

Installation

The exhaust is held in place with bolts just aft of the catalytic converters (red arrows), and a set of brackets/rubber attachment points (second picture) at the rear of the car. The the middle there is a safety/backup hanger (blue arrow) which has a rubber belt around the middle of the exhaust.

Some spray silicone lubricant on the middle bracket may make it easier to slide the belt holding the exhaust off the support. Once this middle connection is free you can remove the front bolts to break the connection to the catalytic converter. Lastly remove the bolts attaching the rubber hangers at the rear of the car.

After removing the stock exhausts, it is time to mount the new Supersprint exhausts. The best way to do this is to first guide the main support into the rubber hanger (blue arrow above) and then to loosely fasten the remaining brackets and bolts. Then, with a couple of people helping, you can align the exhaust and tighten the bolts. (Note that in most cases, we do not recommend hanging from the new exhaust as an alignment method.)

Take your time while adjusting the new exhausts. Even when everything looks fine from under the car, you may still want to tweak the alignment. You want to make sure that the tips are not in contact with the plastic of the rear bumper. Maintain about a finger’s width clearance between the tips and the lower lip of the bumper. Also, stand behind the car and check that each side is symmetrical. As you can see from the picture above, the right tips are slightly rotated clockwise, and need to be adjusted for a better match with the left side.

There were only two negatives to the installation. The first is just due to the inexperience of the reviewer–alignment took a long time. If you have an exhaust shop install your exhaust, this is a non-issue. The second negative is that the new exhausts did not come with 4 necessary nuts and washers. The stock exhaust has nuts integrated into its brackets which bolts go into, while the Supersprint exhaust just has holes in its brackets which bolts go through. This necessitated a quick trip to a hardware store, and cost about $1.00. It is not clear if the missing nuts were an oversight or if they must always be purchased separately, but Supersprint has been notified of this slight glitch and is looking into the issue.

Overall, the installation was uneventful, and took about 2 hours–not bad for a do-it-yourself job. A muffler shop would probably knock out the job in less than half the time. The final result is a set of 4 gleaming tips which emit a healthy growl.

Ok, so it looks and sounds great. Now you want to know about the performance:

Performance

Note: Alamo Autosports is recommended to those in the North Texas area for dyno testing. $60 buys you 3 runs on a Dynojet Dynamometer, worth it just for the experience of seeing and hearing your car dynoed. Contact Brice, Steve Pak, or Steve Webb at

Alamo Autosports

1218 Colorado Ln.

Arlington, TX 76015

817-860-4300

There is a lot of discussion over whether you can improve a car’s performance by replacing the stock exhaust with a “free-flow” aftermarket exhaust. How best to come up with a quantitative answer? With before and after dyno runs, of course.

A day on the dyno at Alamo Autosports in Arlington, TX was scheduled.

Three stock dyno runs were done. They were all close, but the best and worst were thrown out for the purposes of this article. The M roadster, with stock exhaust and no performance modifications, reached a peak rear-wheel horsepower of 217 between 6150 and 6250 RPM. Peak rear-wheel torque was measured at 217 ft./lbs. between 4000 and 4150 RPM. At the bottom of this section of the article is a chart with the full numbers, and the full-size graph of the stock HP and torque curves may be seen by clicking on the small graph at right.

How might an aftermarket exhaust improve performance? By freeing the exhaust flow. This picture shows one way the Supersprint exhaust improves over the stock exhaust. The pipes shown go between the connection at the rear of the catalytic converter and the muffler. The Supersprint exhaust is on top, and the stock exhaust is on bottom. Notice how the Supersprint exhaust pipe takes a straighter path. Also notice how the stock exhaust is somewhat crimped in the middle (to clear a chassis cross-member, which the Supersprint avoids by routing the pipe slightly lower).

After the three “before” runs were completed, the car was driven off of the dyno and allowed to cool. After cooldown, the car was put back on the dyno (used as a lift), and the Supersprint exhaust was installed. After installation was complete, three “after” dyno runs were conducted. Peak torque gain was 6 ft./lbs., and peak HP gain was 5 HP. Since the dyno runs were conducted immediately after the exhaust installation, the numbers reported are for a non-broken-in exhaust. A follow-up set of dyno runs is planned to acquire HP and torque curves for the exhaust after break-in.

Click on the left picture below to hear and see one of the dyno runs after the Supersprint exhaust was installed. The video is of the Supersprint run that produced the highest HP value. Please note that the numbers below are from the middle stock dyno and the middle Supersprint dyno, so the peak HP below is 1 less than the peak HP mentioned in the video.

Click on the right graph below to see the full-size comparison of before and after torque curves. As you can see from the graph, there is a definite increase in torque (important for acceleration) in the entire midrange.

Sound

The Supersprint exhaust produces a deeper and slightly louder sound than the stock exhaust. Do not take this to mean that it is overwhelmingly loud. The Supersprint exhaust meets tough European TUV standards for sound levels. The second-best way to describe the sound is that it makes the M roadster sound like it should sound. The best way to describe the sound, of course, is to let you hear it for yourself. You will need the RealPlayer to hear the audio, if you don’t have the RealPlayer the good news is it is free!.

The sound recordings were made during dyno runs of the stock exhaust and the Supersprint exhaust. A Hi8 camcorder was used to capture the audio, and was placed about 6 feet to the side of the car and slightly behind the car. RealAudio is by no means a crystal clear audio media, but comparing the sound files (Stock vs Supersprint) is a really good comparison of the real life difference. Once the Supersprint exhaust is fully broken in, a “run through the gears” sound sample will be added to this page.